how to run an oversized filter in a small tank

[alweek]

BFG, i'm speaking as a mechanical engineer that happens to deal with filters and pumps....

an impellor or propellor moves water by pushing it. for a propellor, it pushes water behind it. for an filter impellor, it flings the water outwards.

for the filter impellor, the outward flinging action causes a low pressure region to form in the centre/hub region. this draws more water in and the process repeats.

now, when the inlet to a filter is blocked, incoming water cannot rush to fill in the lower pressure region at the hub. this reduced pressure, if it is lower than the vapor pressure of the gases dissolved in the water, can cause the gas to reform from the dissolved state. this occurs at the hub.

these micro bubbles then are swirled around a bit. the moment they move to the outer regions of the impellor (higher pressure), the pressure exceeds the vapor pressure of the gas and they collapse again.

this process of forming bubbles in fluid, whether it is in a submarine OR filter, IS cavitation. it does not have to only happen with a propellor.
cavitation does not need a lot of space to occur. it only needs a region of low pressure so that gas can form.

[BFG]

ah, a mechanical engineer .

In the chamber where the impeller sits, would a vortex appear at the centre of the impeller as the impeller continue to spin but less water is coming in to fill that area and none of the water going out throught the hose? Since the spinning impeller has created a lower pressure in the centre, the outward region has a higher pressure, meaning that more water is collected on the wall of the chamber and the water is still spinning. Now, what if the water that is spinning on the outer area is just 'falling' back to the centre of the impeller and cause some bubbles to form as the water hit the impeller blade ie: water splashes against the impeller blade. Would that happen? Would that scenario also constitute as a cavitation? I was thinking about this because I know for a fact that the impeller has a constant speed in that chamber and by putting your thumb to stop more water from entering the filter, the amount of water should be constant and doesn't increase or decrease. If by somehow the speed of the impeller speed can be increase tremendously, there may be cavitation in that chamber.